Problem

qmd query crashes on longer documents (session transcripts, CJK text, large markdown files) with:

Error: The input lengths of some of the given documents exceed the context size.
Try to increase the context size to at least 2207 or use another model that supports longer contexts.

This affects multiple reported issues: #91, #290, #291, #314

Root cause

Two compounding issues:

1. RERANK_CONTEXT_SIZE = 2048 is too small for documents longer than ~1600 tokens. The Qwen3 reranker template overhead is higher than estimated, so even after truncation, some chunks still exceed the context window.

2. RERANK_TEMPLATE_OVERHEAD = 200 underestimates the actual Qwen3 chat template overhead. Measured at ~350 tokens on real queries; truncation budgets based on 200 allow documents through that still overflow the context.

Fix

• Bump RERANK_CONTEXT_SIZE default from 2048 → 4096
• Make it overridable via QMD_RERANK_CONTEXT_SIZE env var for users with tighter memory budgets or very long documents
• Bump RERANK_TEMPLATE_OVERHEAD from 200 → 512 so the truncation budget correctly accounts for actual template overhead

The 4096 default comfortably fits real-world long documents while staying well below the 40 960-token auto size.